1. Field of the Invention
The present invention relates to a sound-absorbing material, a production method for a sound-absorbing material, and a sound-absorbing structure.
2. Background Art
As a conventional technique relating to a sound-absorbing material, it has been proposed to form a foamable resin binder interposed in a space between fibers to allow fine particles to be held by the fibers, so as to obtain a sound-absorbing material having a Young's modulus of 105 N/m2 or less, as disclosed in JP 08-039596A. Allegedly, the disclosed technique can provide a sound-absorbing material which exhibits excellent sound absorption characteristics in a low-frequency region, and has less performance degradation due to drop-off of the fine particles.
There has also been proposed another sound-absorbing material comprising a porous body having a loss factor of 0.05 or more, an air-permeability value of 0.1 dm3/S or more, and a thickness of 1 to 50 mm, as disclosed in JP 2004-191445A. Allegedly, the disclosed sound-absorbing material can enhance a sound absorption effect in the range of a low-frequency region around 100 Hz to a high-frequency region around 2000 Hz.
As a sound-absorbing structure using a sound-absorbing material, there has been proposed a dome-shaped structure comprising a peripheral sub-structure, and a roof sub-structure, wherein the roof sub-structure includes a first layer formed of a film member, a second layer formed of a sound-absorbing member and located on an outward side of the first layer, a third layer formed of a plate member and located on an outward side of the second layer, a first airspace defined between the first and second layers, and a second airspace defined between the second and third layer, and wherein the film member forming the first layer is made of an air-permeable material to have a flow resistivity of 1×105 to 2×106 N·s/m4, as measured at 20° C. and 1 atm, as disclosed in JP 11-006201A. Allegedly, the disclosed dome-shaped structure exhibits excellent acoustic characteristics, such as sound-absorbing capability, and has an internal space causing less echo generation.
Although each of the JP 08-039596A, JP 2004-191445A and JP 11-006201A discloses a technique of enhancing sound-absorbing capability, the disclosed technique is made with a focus on only a part of physical properties of a sound-absorbing material, such as a flow resistivity, a Young's modulus and a loss factor. That is, these conventional techniques have not been based on thorough consideration on to which of all physical properties of a sound-absorbing material a sound-absorbing capability of the sound-absorbing material is related, and how deeply each of the related physical properties is involved in the sound-absorbing capability. Consequently, their sound-absorbing capabilities over the range of a low/intermediate-frequency region to a high-frequency region are not exactly high.